William crookes



UNITED STATES PATENT OFFICE.

\VILLIAM CROOKES, OF LONDON, ENGLAND.

AMALGAMATING AND EXTRACTlNG GOLD FROM REFRACTORY OR OTHER ORES.

SPECIFICATION forming part of Lette'i's Patent No. 462,535, datedNovember 3, 1891.

Application filed January 10, 1891. Serial No. 377,361. (No model.)Patented in Cape of Good Hope May 28. 1890, N0. 607; in

Natal May 28, 1890; in Transvaal May 28, 1890, N0. 187, and inQueensland September 17,1890, No. 1,039.

To all whom zit may concern:

Be it known that l, WILLIAM CRooKEs, a subject of the Queen of GreatBritain, residing at 7 Kensington Park Gardens, London, England, haveinvented an Improvement in Amalgamating and Extracting Gold fromRefractory or other Ores, (for which I have obtained Letters Patent inNatal under date of May 28, 1890; in the Transvaal underdate of May 28,1890, No. 187; in Queensland under date of September 17, 1890, No.1,039, and in the Cape of Good Hope under date of May 28, 1890,.No.607,) of which the following is a specification.

The present method of extracting gold from refractory ores-such assulphides, tellurides, arseniosulphides, &c., of zinc, copper, iron,bismuth, antimony, &c.by direct amalgamation with mercury is veryimperfect, as the sulphides, arsenio-sulphides, and other minerals inthe ore have a deleterious action on the mercury, causing it to flourand .sicken, so that its fluidity is destroyed, and it becomes either atenacious mass or assumes a powdery character. In either case itsamalgamating action is almost entirely destroyed, with the result thatfrom thirty to eighty or more per cent. of gold escapes the action ofthe mercury, being lost in the tailings, while large quantities ofmercury are also carried off in the washings. The flouring of themercury is due to a film or tarnish from some of the sulphides,arsenio-sulphides, the, coating the mercury and preventing the separateglobules from uniting when once divided by trituration or grinding. Thetrituration in the machines therefore constantly subdivides the mercurymore and more until it becomes a black slimy mass, which will not settlein water for along time, and is carried off in the washings and lost,the separation of this metallic slime from the heavier portions of theore being almost impossible.

The sickening of the mercury is not quite so serious as its fiouring.Sick mercury has taken up some of the constituents of the mineralspresent and has lost its fluidity and will not flow with a brightsurface; neither will it touch gold except with great difficulty.restored by distillation, in which case not much is lost, the chiefdrawback being that sick mercury will not take up gold from the ore; butfloured mercury is not only lost of itself, but it carries away with itall the gold which it may already have taken up. Again, supposing themercury neither flours nor sickens, there is another serious loss whenworkin g with ores containing sulphides, tellurides, arsenic-sulphides,the. Even when the mercury retains its bright metallic condition and isin its usual active state it will seldom take up more than half ortwothirds of the gold present in the ore, owing to the coat of tarnishwhich is almost always on the surface of the gold a coating which canohl y be removed by chemical or mechanical means, the long grindingrequired to remove the coating mechanically then tending to fiour themercury.

Another method of extracting gold from the above-named ores is byroasting till free or almost free from sulphur and then treating with asolvent for gold. The precious metal is then precipitated from itssolution by appropriate means. Chlorine is usually employed for thispurpose;but it is expensive. In some cases cyanide of potassium or asoluble cyanide is used instead of chlorine to dissolve the gold. Thisreagent has, however, a very feeble solvent action on gold, and I canimagine few cases in which a sufficient amount of gold would bedissolved to repay for the expense of the solvent. It has been proposedto remove the tarnish or film (supposed to be sulphide of gold) by theaction of weak nitric acid, nitrate of mercury being present in the bathfor the purpose of amalgamating with the particles of gold as they arecleansed from the film .or tarnish. The drawback to such a process isthat even though the nitric-acid solution be a weak one itwill tend todecompose the more easilyacted on metallic sulphides present, such aslead, iron, zinc, and the like sulphides, and thus liberate sulphuretedhydrogen, which in turn will recoat the particles of gold with asulphide coating. It has also been proposed to use solutions of cyanideof potassium and other soluble salts both with and without a fur- Sickmercury can generally be ther treatment by the electric current; but sofar as I am aware it has always been proposed to use such substances asa solvent for the gold, which is subsequently recovered from itssolution by a further process. Various proposals have also been madewith regard to the use of an electric current, both for the purpose ofassisting the amalgamating and for preventing the flouring or sickeningof the mercury.

The object of my invention is to obviate the disadvantages inherentinthe above processes; and to this end itconsists in submitting therefractory or other ore to the action of a solution,preferablyof cyanideof m ercury,either in the commercially pure state or prepared 'at thetime by double decomposition between a soluble salt of mercury, such asthe sulphate, and the soluble cyanide or ferr0-cyanide. The process isso conducted that the mercurial cyanide shall decompose the film ortarnish on the gold, the cleansed particles of which become amalgamatedwith the mercury as distinguished from becoming dissolved in thesolution, the cyanide of mercury not being a solvent for pure gold. Inlieu of the cyanide the sulphate of mercury can be employed. In manycases I also propose to use in conjunction with the solution of anymercurial salt the current from any alternating dynamo-machine.

In carryingoutmy combined process I proceed as follows: I take the goldore, tailings,

sulphurets, &c., reduced to powder in theusual manner, and mix with thema solution of sulphate, nitrate, chloride, cyanide, or any soluble saltof mercury, and then pass a rapidly-altern atin g current of electricitythrough the mass, either when in a state of rest or when agitated orstirred in any convenient manner. good conductor of electricity, whilethe fine particles of gold sparsely disseminated through the Inass'are,as is well known, excellent conductors. Iron, carbon, or otherconvenient conductors may be used as the poles. Each pole is alternatelycathode and anode. If water is decomposed by such a current, the gasesbeing able to escape do so, and a mixture of hydrogen and oxygen comesfrom each pole. If, however, the results of the decomposition are fixed,such as acid and metal, the decomposition by the current in onedirection is reversed by the following current in the opposite directionand practicallylittle or no decomposition results. Assume that sulphateof mercury is the mercurial salt chosen. Then when the pole with whichitis in contact becomes positive sulphuric acid is there liberated,while mercury is liberated at the opposite pole; but in a fraction of asecond the poles are reversed, the opposite decomposition is eifected,and the sulphuric acid just liberated finds itself in presence ofnascent mercury, with which it immediatelyconr bines. At the other polethe mercury liberated by the first current finds a molecule of The bulkof the massis not a very sulphuric acid ready to reunite with it, and soat each pole the mercurial salt is decomposed onlyto be immediatelyreunited. Every particle of gold in the wet mass through which thealternating current is passing is a much better conductor of electricitythan the surrounding mass, and the equipotential, lines of force willconverge toward them, with the result that more of the electric currentpasses through them than through the rest of the mass, and the two sidesof each particle of gold act alternately as anode and cathode. On oneside (the anode for the time being) sulphuric acid is liberated, and onthe other side (the cathode for the time being) mercury is liberated;but the affinity of gold for mercury is so great that the twometalsinstantly unite and the gold becomes amalgamated.

. At the next alternation the side of the gold particle which had thesulphuric acid liberated on it now has the mercury precipitated on it.The affinity of gold for mercury here again comes into play, and insteadof reuniting with the sulphuric acid the mercury prefers to attack thegold. Thus each alterna tion precipitates mercury on alternate faces ofthe particles of gold in the mass of ore without requiring the gold tobe in metallic communication with either pole of-the dynamo, as theextra conductivity of the gold draws to it the lines of force. The sizeof the particles is not essential, as the finest flour and float goldwill be amalgamated, and consequently Weighted, as easily as the largestpieces. Neither does it matter to what degree of coarseness the ore iscrushed so long as the solution of the mercurial salt penetrates to onepart of the piece of gold locked up in the ore, for the action will thentake place and the metal will become amalgamated and in thesubsequentamalgamating operation dissolved in the mass of mercury.

A further advantage incidental to the use of an alternating current isthat the sudden and violent decompositions and recompositionsalternating with great rapidity cause the mass to become hot, therebygreatly -facilitating the amalgamation.

Any ordinary alternating current from an alternating dynamo or othersource-of electricity will produce the desired effect; but the mostefficient action is dependent on the right adjustment of severalvariable factors, such as, first, current density; second, area ofelectrodes; third, rate of alternation per second; fourth, electricconductivity of the wet mixture of crushed ore and liquid. The lattervarying with every different kind of ore, itis evident that the otherswill have to be adj usted in each separate case in order to get themaximum effect, and that therefore no general directions can be heregiven which will meet all cases.

When it is impracticable to use an electric current, I propose to employa solution of cyanide of mercury or a sulphate of mercury, either IIO ofwhich solutions will remove the film or tarnish and superficiallyamalgamate the particles of gold. The process will not, however, be sorapid as it is when the alternating electric current is used, althoughit may be hastened somewhat by heating the mass. When carrying out theprocess in this mannerI propose to use a solution composed of two orthree pounds of cyanide of mercury or of sulphate of mercury dissolvedin eighty to one hundred gallons of water for each ton of ore; butspecial circumstances may render it advisable to vary these quantities.When the action is complete, the mercury solution may be drained ordrawn off or removed in any other convenient Way and the ore treated inamalgamating pans or machinery or in other appropriate manner.

In some cases I find it an advantage to add to the mercury used for thesubsequent amalgamation process a little amalgam of sodium, as describedin my British specification No. 391 of 1865, or some of the modifiedamal' gams described by me in my British specification No. 2,229 of1865.

It will be evident that the mercurial salt, either alone or inconjunction with the amalgams just referred to and with or without theuse of the alternating electric current, may be employed in the grindingand amalgamating apparatus, and in this case the cleansing of the goldfrom the tarnish or film and the collection and amalgamating of thecleansed particles may go on simultaneously. When this is desired, freshmercury should be added to the mass and thoroughly mixed or incorporatedtherewith. The solution of mercurial salt and an alternating current mayalso be advantageously employed in concentrating and vanning machines,such use causing the gold particles to unite more readily with themercury.

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatWhat I claim is- 1. The improvement in the process of amalgamatiug andextracting gold hereinbefore set forth, which consists in submitting theore to the combined action of a solution of a mercurial salt and analternating electric current, substantially as described.

2. Theimprovement in the process of amalgamating and extracting goldhereinbefore set forth, which consists in submitting the material in thefinal amalgamating process to the combined action of a solution of amercurial salt and an alternating electric current, substantially asdescribed.

In testimony whereof I have hereunto set my hand in the presence of twosubscribing witnesses.

WILLIAM CROOKES.

Witnesses:

ALLEN P. J oNEs, JAMES Bonus.

